In an image forming apparatus such as a laser printer, an electrostatic copying machine, a plain paper facsimile machine or a printer-copier-facsimile multifunction machine, a separation pad is generally used for separating and feeding out a sheet from a stack of sheets contained in a sheet feed cassette or a sheet feed tray (the term “sheet” is herein defined to include a paper sheet, a plastic film such as an OHP film and the like, and this definition is effective in the following description). Further, a sheet feed roller for feeding the sheet and a registration roller for registering a leading edge of the sheet and feeding out the sheet at predetermined timing are used in combination with the separation pad.
Sheet feeding members including the separation pad, the sheet feed roller and the like are conventionally produced by forming a rubber composition containing a crosslinkable rubber into a predetermined shape and crosslinking the rubber (Patent Literature 1).
In recent years, however, it has been required to use a thermoplastic elastomer for the production of the sheet feeding members because the thermoplastic elastomer has a thermoplastic property and hence is easy to recycle (Patent Literature 2).
To meet recent requirements for size reduction and cost reduction of the laser printer and the like, the construction of a sheet feeding mechanism itself is simplified with the need for reduction in the number of parts.
In the conventional sheet feeding mechanism, a sheet is separated and fed out from the stack of sheets contained in the sheet feed cassette or the like by the separation pad and the sheet feed roller, and then transported to an image forming section through the registration roller, a sheet transport roller, an anti-static brush and the like.
In the conventional sheet feeding mechanism, therefore, the separation pad is repeatedly rubbed against sheets to be electrically charged, and the accumulated electric charges are often released to the sheet, which is in turn electrically charged. However, the electric charges are removed from the sheet when the sheet is transported along a transportation path provided with the various rollers before reaching the image forming section. Therefore, the image formation is not influenced by the electric charges.
In an image forming apparatus having the simplified sheet feeding mechanism, however, the electric charges are not sufficiently removed from the sheet, so that the sheet is fed into the image forming section in a charged state. This frequently results in formation of a disturbed image.
In order to prevent the formation of a disturbed image, it is desirable to produce the separation pad from a material such that the surface potential of the separation pad can be maintained at a lower level even if the surface of the separation pad is repeatedly brought into contact with sheets to be rubbed against the sheets.
In the present invention, the surface potential is expressed as a value determined by the following measurement. A surface of a separation pad forming material is electrically charged in an ordinary temperature and ordinary humidity environment at a temperature of 23° C. at a relative humidity of 50% by reciprocating the separation pad forming material for a distance of 30 mm at a speed of 3000 mm/min 30 times with the surface of the separation pad forming material kept in contact with a proper bond paper sheet (Canon's PB PAPER) with a load of 1.96 N by means of a surface state analyzer (TRIBOGEAR (registered trade name) HEIDON (registered trade name) 14DR available from Shinto Scientific Co., Ltd.), and then the surface potential of the separation pad forming material is measured by means of a compact surface potentiometer (KASUGA KD-103 available from Kasuga Electric Works Ltd.)